The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides an annulus pressure referenced circulating valve.
It is well known in the art to operate a valve positioned in a subterranean well by applying fluid pressure to the valve. The fluid pressure may exist by virtue of the weight of fluid in the well, the fluid pressure may be applied to the valve by, for example, a pump at the earth's surface or in the well, and the fluid pressure may be a combination of these. When the valve is interconnected in a tubular string positioned in a wellbore of the well, the fluid pressure may exist in the tubular string, in an annulus formed between the tubular string and the wellbore, or the valve may be operated by a difference between fluid pressure in the tubular string and fluid pressure in the annulus.
Where a valve is operated by absolute fluid pressure in a tubular string or in an annulus exterior to the valve, the valve typically includes a chamber at atmospheric pressure or an elevated precharged pressure at the earth's surface. After positioning in the well, a fluid pressure differential (equal to the difference between the chamber pressure and the pressure in the tubular string or annulus) is generally created across a member releasably secured against displacement by, for example, one or more shear pins. When a predetermined fluid pressure differential is reached, the member is released and displaced by the differential pressure, thereby operating the valve. Unfortunately, however, it is often uncertain what pressure conditions will be experienced in the well prior to installing the valve in the tubular string, so there is a danger that the valve will be inadvertently operated due to an unexpected pressure increase in the tubular string or annulus.
Where the valve is operated in response to a pressure differential between the tubular string and the annulus, the member is typically released for displacement when the predetermined fluid pressure differential is created. While, strictly speaking, operation of this type of valve does not require prior knowledge of absolute fluid pressures in either the tubular string or annulus, it does requires prior knowledge of fluid pressures to be experienced in both the tubular string and the annulus, so that the fluid pressure differential may be determined and the valve may be set up to avoid inadvertent operation of the valve.
Solutions to the problem of inadvertent operation of pressure responsive valves have been implemented. For example, it is common for a valve to include a chamber at an elevated pressure and a member displaceable in response to a difference in pressure between the chamber and the tubular string, the annulus, or a difference between the tubular string and annulus pressures. By manipulating the tubular string pressure, the annulus pressure, or the difference between the tubular string and annulus pressures, the member is made to displace repeatedly, the member displacing sufficiently to operate the valve after a predetermined number of the pressure manipulations. The number of pressure manipulations is usually determined by a ratchet or J-slot mechanism. Unfortunately, this type of valve requires numerous pressure manipulations, and a complex and expensive ratchet or J-slot mechanism.
Therefore, it would be highly desirable to provide a valve responsive to fluid pressure in a well, which does not require numerous pressure manipulations or precise prior knowledge of fluid pressures to be experienced in the well, and which is relatively uncomplicated in its construction and use.